Screening outcomes at second FIT screening in individuals with a first time negative FIT-result or low-risk adenomas: Results from a nationwide FIT screening program

In Denmark, participants in faecal immunochemical test (FIT) screening with low-risk adenomas are recommended a return to biennial FIT-screening. However, they participate less than the FIT-negative group (FIT1-negative) at subsequent screening. Further, it is not clear how much this group benefits from the subsequent screening. We aimed at comparing the CRC incidence before and at the next screening (FIT2) in the low-risk group to that of those having a FIT-negative result at first time FIT-screening. In this register-based cohort study, we estimated the incidence of interval CRC (ICRC) and results of FIT2, including the FIT2-positivity rate and rate of screen detected CRC (SDCRC). Relative risk (RR) comparing the low-risk group to FIT1-negatives was estimated. Adjustment for age and sex was performed with binary regression and presented with a 95% confidence interval (CI). Incidence of ICRC was 0.17% and 0.08% in the Low-risk group and FIT1-negative group, respectively, RR 2.18 (95%CI 1.51; 3.16). After adjustment, RR was 1.76 (95%CI: 1.22; 2.55). The FIT2-positivity rate was 14.4% and 4.4% for the Low-risk group and FIT1-negative group, respectively. At FIT2-screening, the detection of SDCRC was 0.36% and 0.16% in the low-risk and FIT1-negative group, respectively, RR 2.27 (95%CI: 1.46; 3.54), adjusted 1.83 (95% CI: 1.17; 2.85). Despite a recent colonoscopy, participants having low-risk adenomas detected at first colonoscopy in FIT-screening remain at a higher short-term risk of ICRC and SDCRC compared to the FIT1-negatives. Continuous participation in FIT-screening is important for the Low-risk group.